Security experts said the attack in France, in which a driver mowed down scores of people during Bastille Day celebrations, will heighten security concerns

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Barriers divide ninth street in downtown Cleveland, Ohio, on July 14, 2016, marking the secure zone surrounding the Quicken Loans Arena, site of next week's Republican National Convention.

Security planning for the Republican and Democratic national conventions took into account large-scale threats like the vehicle attack that occurred in France and left dozens dead and wounded, a U.S. Secret Service official said Friday.

"There is nothing we leave to chance," said James Henry, the agency's special agent in charge in Philadelphia.

Planning for the Democratic National Convention in Philadelphia began in October, and security measures cover everything from people jumping fences to organized attacks, he said.

Agents will sweep permitted vehicles for explosives and turn away general traffic in security zones set up around the convention sites. Philadelphia police will use rolling street closures and uniformed officers to protect areas outside the security zone where large protests and rallies are planned.

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In Cleveland, federal officials have already restricted road, air and water travel around the city for next week's Republican National Convention, with security measures affecting passenger and cargo vehicles.

Officials declined to comment on specific changes following the attack in Nice. Cleveland Mayor Frank Jackson expressed his condolences to the friends and families of the victims.

The Plain Dealer reported Friday that scores of paramedics, doctors and nurses will be stationed in and around Quicken Loans Arena in downtown Cleveland during the four-day convention to handle everything from minor injuries to multiple casualties. The medical plan was developed over several months.

The city was a study in contrasts Friday afternoon. Even as restaurants and bars filled up with the usual Friday post-work patrons, large tents were being erected outside the arena, dubbed the Q.

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Drivers headed into downtown saw signs urging people to call an FBI tip line if they see anything suspicious. A tall security fence was going up along several blocks of East 9th Street in the heart of downtown. Garbage cans were replaced with clear plastic bags hanging from metal supports.

Overhead, a plane pulled a sign that read "Rescue Unborn Children" with the letters RNC — for Republican National Convention — highlighted in red.

Ricky Stokes, 54, a downtown resident, said he's comfortable with security, saying the city's been transparent with its preparations by providing town hall briefings with security officials on what to expect.

A friend, Virnette House, of suburban Westlake, who works at nearby Cleveland State University, said she also feels safe but added the events in France have led to heightened awareness.

"Walking through today I didn't see as many police officers as I thought there should be," said the 20-year-old Fields, of Cleveland.

Security experts said the attack in France, in which a driver mowed down scores of people during Bastille Day celebrations, will heighten security concerns. But they note possible countermeasures, like establishing static, barricaded zones, can pose their own risk by creating concentrated targets.

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The use of rolling street closures can help law enforcement by keeping routes open for emergency responders, allowing police to manage crowd movement and prevent static zones that can become targets for an attack, said Edward Clark, homeland security expert and principal consultant for Executive Interface LLC, a security consulting group.

Security details are also often advised to keep groups small, create multiple entrance points to specific gathering areas and stagger attendance, he said.

Henry Willis, director of the Rand Corp. Homeland Security and Defense Center, said security organizations each have unique capabilities and responsibilities, which can create seams in protection.

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Making her first public appearance Wednesday evening since her emotional concession speech a week earlier, Clinton said: "It's up to each and every one of us to keep working to make America better and stronger and fairer." (Published Thursday, Nov. 17, 2016)